4去5入到指定位数

function my_round(num, how)
{
if (isNaN(num))
{
return 'N/A';
}

if (isNaN(how)) return num;
if (how < 1) return Math.round(num);

var splits = num.toString(10).split(".");
if ( (splits.length != 2) || (splits[1].length < (how + 1)))
{
return num;
}
else
{
how = Math.pow(10,how);
return Math.round(num * how )/how ;
}
}